This invention relates to visual indicating devices and more particularly to visual indicating devices of the type adapted to indicate the position of an automatic transmission lever in an automotive vehicle.
All automotive vehicles which have an automatic transmission include a means for visually indicating the position of the transmission shift lever within the predetermined sequence of positions provided. The usual situation is to provide an indicating means which is mechanically connected with the lever to provide an indication based upon the particular position of the lever. A typical example in this regard is to provide a pointer which is essentially fixed with respect to the lever to move through an indicating area containing distinctive characters representative of the sequence of positions so that, as the lever is moved through the sequence of positions, the pointer will point to the distinctive character representative of that position. Usage over a number of years has established the usage of "P" for the parking position, "R" for the reverse position, "N" for the neutral position, and "D" for the drive position. Where there are only two drive positions, the other drive position is indicated by an "L". Where there are three drive positions, the other two are designated by the numerals "2" and "1". A typical sequence is "PRNDL" for two drive position transmissions and "PRND21" for three drive position transmissions. In recent years, transmissions have been provided with an overdrive capability constituting a fourth forward speed and, when the lever is moved into the overdrive position, the distinctive character utilized is "OD". In this instance, the usual sequence is "PRNODD21".
There are several problems associated with a visual indicating arrangement which is dependent upon the physical position of the shift lever to indicate the position of the shift lever. The primary disadvantage is a lack of accuracy in alignment of the pointer with the indicia due to the mechanical characteristics of the arrangement. In situations where adjustment is required after installation, significant costs are accrued to make the necessary adjustment. Another disadvantage is that there may be insufficient lighting to provide the visibility for the physical pointer itself. Moreover, severe limitations as to the position and shape of the indicating device in the vehicle are imposed by a strictly mechanical indicating arrangement.
As early as 1977, there have been proposals in the patent literature which would have the effect of obviating certain of the disadvantages noted above. In U.S. Pat. No. 4,037,196, there is disclosed a visual indicating arrangement for automotive vehicles, particularly those having five or more forward speeds such as are embodied in trucks or the like. The patent describes the provision of a number of microswitches mounted on the housing for engagement with the shift bars of the transmission. The arrangement further contemplates that the microswitches are connected to a coder which generate binary coded decimal signals representing the shift lever position and the output of the coder is used to drive a seven-segment light emitting diode (LED). Despite the early suggestion of a seven-segment LED digital display unit as the visual indicator for a device of the present type, to date there has been no utilization of such a system as far as applicant is aware.
In the intervening years, it has become common practice to provide electrical signals which are indicative of the condition of the transmission, which electrical signals are utilized in the computer control of the engine. In two recently issued patents, namely U.S. Pat. No. 4,882,572 and 4,896,135, it has been proposed to utilize the signals normally generated for use with the engine control computer in an arrangement for visually indicating the position of the transmission shift lever so as to obviate the problems relating to mechanical arrangements noted above. The provision in both of these patents is to provide a logic circuit which will receive the normally provided signals and to provide an output signal which is indicative of each of the positions of the shift lever and to turn on a liquid crystal display in accordance with the output signals. In each of the patents, the output signal is transmitted to a liquid crystal display which serves as the visual indicator for the device. Here again, even though the two patents are assigned to Delco and General Motors respectively, to date there has been no commercial utilization of a liquid crystal display in actual commercial operation. Consequently, there still exists a need for a cost effective display device which will obviate the disadvantages of the mechanical pointer type indicating device heretofore utilized.